<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>测试</title>
</head>
<body>
    <script>
        for(var j = 0; j < 4; j++) { // validate the operator 验证运算符是否有效
            if(j == 2) {
                break;
            }
        }
        if(j >= 0) {
            console.log('j = ' + j); // 2
        }

        var array = [];
        console.log('array = ' + array.pop());
    </script>
</body>
</html>